onsemi BC309CBU

Overview

BC309CBU from Fairchild Semiconductor is a PNP epitaxial silicon transistor optimized for low-noise amplifier and switching applications, with confirmed hFE classification C (380–800), V_CEO = −25 V, I_C = −100 mA, P_C = 500 mW, and f_T = 130 MHz - deployed in audio preamplifier stages and signal conditioning circuits where noise performance is critical.

For engineers reviewing the BC309CBU datasheet, pinout, applications, or equivalent options, key selection considerations include its low-noise figure (4 dB at 30–15 kHz), TO-92 package compatibility, hFE Class C gain range, saturation voltage behavior under −10 mA/−0.5 mA drive, and V_BE(on) of −0.55 to −0.7 V at −2 mA collector current.

Technical Context

The BC309CBU operates as a general-purpose PNP bipolar junction transistor with epitaxial base construction enabling stable high-frequency response and low 1/f noise. Its hFE Class C specification ensures consistent DC current gain between 380 and 800 at V_CE = −5 V and I_C = −2 mA, supporting precision biasing in linear amplifiers.

Designed for operation in the active and saturation regions, it delivers V_CE(sat) ≤ −0.5 V at I_C = −10 mA/I_B = −0.5 mA and ≤ −0.3 V at I_C = −100 mA/I_B = −5 mA, while maintaining Cob = 6 pF and Cib = 12 pF - enabling predictable RF and audio-stage impedance matching.

Key Specifications

Pinout & Package

BC309CBU uses a standard TO-92 package with three leads: Collector (lead 1), Base (lead 2), Emitter (lead 3), arranged in straight-line configuration per Fairchild Rev. A2 mechanical drawing.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP small-signal transistor applications.

Compared with BC309CBU, BC327-40 offers greater voltage headroom but sacrifices low-noise assurance and high-gain consistency, while MMBT3906LT1G provides SMT compatibility and higher bandwidth at the cost of unverified audio-band noise performance and non-pin-compatible packaging.

Availability

BC309CBU is available at Aetrix Electronics and suitable for audio preamplifier design, discrete-level translation circuits, and DC power sequencing applications requiring stable component supply, long-term obsolescence management, and traceable sourcing.

Supply support for BC309CBU includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Fairchild Semiconductor was a U.S.-based semiconductor manufacturer specializing in discrete power and analog components before its acquisition by ON Semiconductor in 2016.

The BC309CBU belongs to Fairchild's legacy BC307/308/309 PNP transistor family, designed for general-purpose amplification and switching in consumer, industrial, and communications equipment where TO-92 compatibility and gain binning were essential.

FAQ

What does the 'C' suffix in BC309CBU indicate?

The 'C' in BC309CBU denotes hFE Class C, specifying a DC current gain range of 380 to 800 at V_CE = −5 V and I_C = −2 mA. This binning ensures tighter gain consistency across production units compared to Class A (120–220) or Class B (180–460). The 'BU' suffix indicates TO-92 packaging with standard lead formation. BC309CBU thus guarantees predictable biasing in amplifier designs without post-selection.

Is BC309CBU suitable for low-noise audio applications?

Yes - BC309CBU is explicitly characterized for low-noise performance: 4 dB noise figure measured at V_CE = −5 V, I_C = −0.2 mA, R_G = 2 kΩ, and 30–15 kHz bandwidth. This specification distinguishes it from BC307 and BC308 variants and makes BC309CBU appropriate for microphone preamps, tone controls, and other audio front-end stages where self-noise directly impacts signal fidelity.

What is the maximum continuous collector current for BC309CBU?

The absolute maximum continuous collector current (I_C) for BC309CBU is −100 mA at T_A = 25°C. Derating applies above 25°C: approximately −0.8 mA/°C beyond 25°C ambient, based on the 500 mW total power dissipation limit and thermal resistance of the TO-92 package. Operation at −100 mA requires adequate PCB copper area or airflow to maintain junction temperature below 150°C.

Can BC309CBU replace BC309B or BC309A in existing designs?

Yes - BC309CBU is pin-compatible and electrically interchangeable with BC309A and BC309B, differing only in hFE binning (A: 120–220, B: 180–460, C: 380–800). No PCB or schematic changes are needed. However, higher hFE may alter bias point stability in marginal designs; verify quiescent operating point and thermal margin if substituting into legacy BC309A/B circuits.

Does BC309CBU have a documented Safe Operating Area (SOA) curve?

No SOA curve is provided in the Fairchild BC307/308/309 Rev. A2 datasheet. Designers must rely on absolute maximum ratings - including V_CEO = −25 V, I_C = −100 mA, and P_C = 500 mW - and apply conservative derating for pulsed or transient conditions. For applications involving inductive loads or voltage spikes, external clamping or snubbing remains necessary, as BC309CBU lacks built-in protection features.